Disagreements among the countries backing the rebels in Syria have led to a drop in weapons shipments, leaving rebels vulnerable to a government military offensive.

The precise nature of the dispute is unclear, but one of the effects is that Saudi Arabia has stopped sending weapons via Turkey and has shifted its supply channels to northern Jordan. The result has been fewer guns and bullets for the rebels in northern and central portions of the country.

The lack of military supplies has shown in the rebels’ lackluster performance against a government offensive that now threatens the city of Qusayr, which has been in rebel hands for the past year. Several villages near Qusayr have fallen to government forces in recent weeks along a smuggling route that rebels had long used to move supplies and people into Syria from Lebanon.

Yazed al Hasan, a spokesman for the Farouq Battalions, a rebel group that began in the central Syrian province of Homs but whose influence now extends to the Turkish border, where it controls two crossing points, said the consequences of the drop in shipments from Turkey was clear.

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“The shortage of ammunition means losing the Qusayr front,” he said. He said Farouq had more than 1,000 fighters in Qusayr, which is now largely surrounded by Syrian soldiers and pro-government militia. Last week, the U.S. State Department issued a statement expressing concern that the Syrian government had dropped leaflets telling “all civilians to evacuate or be treated as combatants.”

A week visiting rebel frontlines in northern and central Syria found that the drop in weapons shipments had disproportionately affected rebel groups allied with the Supreme Military Council, the rebel faction that the U.S. has selected as a conduit for lethal and nonlethal aid sent to Syria by the United States and its allies. At the same time, groups that advocate the establishment of an Islamic state in Syria should the government of President Bashar Assad fall seemed to be unaffected.

That has left the rebels who pledge allegiance to the Supreme Military Command and advocate a civil government in the wake of Assad’s fall in the uncomfortable position of having to rely on more radical groups for support.

Yousef Hassan, a commander in the Grandsons of the Prophet Brigade, said that he was allied with the Syrian Military Command, which is led by a defected Syrian general, Salim Idriss. Hassan said that he’d told Idriss’ staff about an assault by dozens of his fighters on a military airport in northern Syria last week.

But Hassan had planned the operation with a religious extremist rebel faction, Ahrar al Sham, which advocates an Islamic state in Syria. Those men, led by a commander named Dabbous, had brought mobile rocket launchers to the battle in order to support Hassan’s men as they attacked the airport’s main gate in an assault that ultimately failed. Ahrar al Sham does not recognize Idriss’ command, though Dabbous said his battalion had received aid from it.

An American official who met recently with a representative of Idriss’ movement acknowledged that not all weapons being provided by some countries that the U.S. considers allies in Syria are going to Idriss’ group, despite an agreement last month that both lethal and nonlethal assistance would be funneled through the Supreme Military Command. The official, who asked not to be identified because of the sensitivity of the subject, said the supply situation was the topic of ongoing conversations with those nations, though he did not identify the nations.

An official of the Syrian Opposition Coalition, the civilian organization that the United States and scores of other countries now recognize as the legitimate opposition front, was less circumspect, however.

Khaled Khoja, the coalition’s spokesman, said money and weapons are still flowing to the Nusra Front, a group the United States has said is just another name for al Qaida in Iraq. He said Saudi Arabia and Kuwait have cut Nusra off but that the group is still receiving money from elsewhere.

“The Saudi and the Kuwaiti states are very strict on not funding the Islamists,” he said. “Qatar is bolder.”

He said Nusra also continues to receive money from private individuals. He said that the Saudi government had attempted to crack down on support being sent to rebel groups through unofficial channels, but that other countries, including Kuwait, had not done so effectively.

Trying to isolate Nusra from other rebel groups has become a central objective of U.S. officials since the U.S. designation in December of Nusra as a terrorist organization. That’s one reason the U.S. last month reached the agreement with other countries to route aid through Idriss’ Supreme Military Command, whose members tend to describe themselves as “thowar” – Arabic for revolutionaries – rather than “mujahedeen,” which translates as “holy warriors,” the term favored by Islamist factions.

But the impact of that effort is uncertain, since the ability of Idriss’ group to provide supplies is largely untested.